Nano-silicon composite negative electrode material used for lithium ion battery, process for preparing the same and lithium ion battery

Abstract

The present invention relates to a nano-silicon composite negative electrode material, including graphite matrix and nano-silicon material homogeneously deposited inside the graphite matrix, wherein the nano-silicon composite negative electrode material is prepared by using silicon source to chemical-vapor deposit nano-silicon particles inside hollowed graphite. The nano-silicon composite negative electrode material of the present invention has features of high specific capacity (higher than 1000 mAh / g), high initial charge-discharge efficiency (higher than 93%) and high conductivity. The preparation process of the present invention is easy to operate and control, and has low production cost and is suitable for industrial production.

Description

TECHNICAL FIELD[0001]The present invention belongs to the technical field of lithium ion battery, and specifically relates to a nano-silicon composite negative electrode material used for lithium ion battery, a process for preparing the same and a lithium ion battery.BACKGROUND ART[0002]Lithium ion battery is an ideal power source for portable electronic equipments, electric vehicles, energy storage systems. It is the core of the research and development field of the lithium ion battery to develop a novel electrode material having high specific energy, better safety and low cost. Studies on novel negative electrode materials have an important meaning to the development of new-generation lithium ion battery. The negative electrode materials of the current mature lithium ion battery are mainly graphite materials having a theoretical specific capacity of 372 mAh / g and limited developing potential, and thus cannot meet the demand of the future lithium ion battery on high-energy density....

AI Technical Summary

Benefits of technology

[0011]The nano-silicon composite negative electrode material of the present invention is characterized in high specific capacity, high initial charge-discharge efficiency and high electrical conductivity.

[0022]By homogeneously depositing nano-silicon particles inside hollowed graphite material according to the preparation process of the present invention, the inner voids of the hollowed graphite provide much space for loading the nano-silicon, which may effectively increase the loading capacity and the dispersibility of the nano-silicon in the negative electrode material. The chemical vapor depositing method can form monodispersed nano-silicon particles inside the graphite material and avoid secondary agglomeration of the nano-silicon material. Moreover, the chemical vapor depositing method can also avoid surface oxidation of the nano-silicon material and increase the initial charge-discharge efficiency of the negative electrode material.

[0027](4) Proceeding the material obtained in step (3) to nano-conductive material coating modification; enhancing the contact between the conductive material and the composite material and increasing the conductive performance of the composite material by coating the nano-conductive material on the surface of the composite material;

[0040]Preferably, the coating modification in step (4) is one selected from the group consisting of mechanical modification, nano-dispersion or liquid phase coating. The mechanical modification, nano-dispersion or liquid phase coating may promote homogeneous dispersion of the nano-conductive material on the surface of the composite material and avoid agglomeration of the nano-conductive material.

[0042]The preparation process of the present invention can also be used for preparing the nano-silicon composite negative electrode material of the present invention, and can achieve better effects.

[0044]The nano-silicon composite negative electrode material of the present invention has features of high specific capacity (higher than 1000 mAh / g), high initial charge-discharge efficiency (higher than 93%) and high conductivity. The preparation process of the present invention is easy to operate and control, and has low production cost and is suitable for industrial production.

Problems solved by technology

The negative electrode materials of the current mature lithium ion battery are mainly graphite materials having a theoretical specific capacity of 372 mAh / g and limited developing potential, and thus cannot meet the demand of the future lithium ion battery on high-energy density.

However, such negative electrode material has a greater lithiation / delithiation volume expansion and shrinkage (>300%), and high volume effect renders worse cycle stability, resulting in that there is a certain distance between these systems and practical level.

The aforesaid structures both involve coating nano-silicon onto the surface of graphite particles, which easily result in uneven distribution of the nano-silicon, being unable to effectively use the space inside the graphite particles, and being unable to further increase the loading capacity of the nano-silicon.

However, the nano-silicon particles are very easy to agglomerate during the drying, and thus cannot form the very homogeneous and monodispersed composite state of the nano-silicon particles inside the hollowed graphite.

The agglomerated nano-silicon will gradually fuse during the charge and discharge process to form large-grained silicon, and the cycle and expansion performance will notably degrade.

However, common porous carbon material (e.g. activated carbon) has too small voids to effectively support nano-silicon material.

The carbon nanotube or graphene itself is easy to agglomerate, and thus cannot achieve homogeneous deposition of nano-silicon material on the surface thereof.

If the nano-silicon material has a too low content in the negative electrode material, it will has a low specific capacity; if the nano-silicon material has a too high content in the negative electrode material, it will has a high cycle expansion.

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